Many homes around the world use solar systems for the supply of hot water. For example, in Israel there are estimated to be more than two million such systems.
In Israel, installing such a solar water heating system in the home is required in building codes and regulations. According to the law, any building less than ten floors high must include a solar water heating system.
In Israel, there are two main types of domestic solar water heating systems:
An open system:
In such a system, each apartment has an independent solar unit, in which the water is heated for the apartment. Cold water enters a solar panel, where it is heated by the heat of the sun, and then it is conveyed to a hot water tank. This system is highly efficient and is in use in private homes and apartment buildings less than four floors tall.
A closed system, including a heat exchanger:
In high-rise apartment buildings, there is not enough roof space to provide each apartment with an independent solar unit. In order to meet the requirement of Israeli law, a common solar system was developed for apartment buildings.
FIG. 1 of the prior art is a side view schematic illustration of a hot water supply system 2 installed in a multi unit apartment building 1.
FIG. 2 of the prior art is a side view exploded schematic illustration of a hot water supply system 2.
The hot water supply system 2 also includes a heat exchange solar system 3, which includes a solar panel 11, (or solar panels), from which hot water flow through a hot heating fluid pipe line 12.
From the hot heating fluid pipe line 12, one heating fluid input pipe line 13 branches out for each internal heat-exchanger 14.
In the course of the flow of the heating fluid (not shown in the illustrations), heat is exchanged, the water 22 in the boiler 21 is heated, while the heating fluid is cooled.
From each internal heat-exchanger 14, heating fluid flows in a heating fluid output pipe line 15 and onward returns to the solar panel 11 through a cold heating fluid pipe line 16.
Often, the heat exchange solar system includes a pump 17, which facilitates the flow of the heating fluid. Pump 17 is active when the heating fluid at the top part of the solar panel 11 is hotter than the heating fluid at the bottom part of the solar panel 11 (namely, solar heating is taking place). When this condition is not in place, pump 17 ceases action, and the heating fluid flows according to the laws of connected vessels and preservation of energy.
Water 22 is provided at a sufficiently high pressure for each boiler 21 through a cold water pipe line 23.
Water 22 from a boiler 21 is provided for use through a hot water pipe line 24 when a faucet 25 is opened. When the hot water supply system 2 cannot supply water 22 at a sufficiently hot temperature, every apartment unit can heat the water 22 in its separate boiler 21 by activating an electrical heater 26.
The hot water supply system 2 has a major disadvantage of heat loss through the internal heat-exchangers 14. There are cases in which a tenant activates an electrical heater 26, the water 22 is heated, and if the temperature of the water heated electrically is higher than that of the heating fluid, there is a negative exchange of heat, namely heat from the water 22 is transferred to the heating fluid.
An additional disadvantage is natural heat loss at sunset and after the hot water supply system 2 heated the water 22 in each boiler 21 throughout the day by means of solar energy. A slow process of heat loss from each boiler 21 to the hot water supply system 2 occurs even when pump 17 is inactive.
The slow process is caused by physical action of the laws of connected vessels and energy preservation. There is movement of the water 22 even without activation of the pump 17. Water 22 that is hotter in some of the apartments in the building will flow to apartments in which the water 22 is colder, causing eventual heat loss for all apartments in the building. Namely, the cumulative effect is that the water 22 in each boiler 21 cools over the night.
An additional disadvantage is a result of the method of activation of the pump 17. The pump 17 is activated based upon measurement of a maximum point of the heat exchange solar system 3. Following this principle, it could also act when there is no effective heat from the solar panel 11, for example on a cloudy day, the activation equation for the pump 17 can apply (the heating fluid at the top part of the solar panel 11 is hotter than the heating fluid at its bottom), however, there will not be effective heating of water 22 in reasonable quantities for the entire building. In this case, heat generated by the tenants of the building by means of each boiler 21 will quickly be transferred into the hot water supply system 2 and impair the efficiency of the apartment heating, while wasting energy resources and tenants' money.
There is therefore a need for a new solution to overcome the present disadvantages of the existing hot water supply system 2.